1. Field of the Invention
The present invention relates to a space photovoltaic power generation method of receiving sunlight in space so as to generate electric power, for transmitting the electric power via space by converting the electric power to microwaves, and for receiving the microwaves on the earth so as to allow the use of the electric power. More particularly, it relates to a method of and a system for receiving the microwaves.
2. Description of the Prior Art
With an increase in the demand for electrical energy in recent years and attaching importance on environmental issues as a background, the development of clean, safe, and stable power supply equipment is an urgent necessity. Attention has been focused on the idea of space photovoltaic power generation systems according to such a request, and the research and development has been conducted actively. Space photovoltaic power generation systems receive sunlight in space, generate electric power, and transmit the electric power to a specific place, for instance, a specific location on the earth or in space.
As an example of space photovoltaic power generation systems, a method of placing a plurality of geostationary power satellites in predetermined different positions in space, converting (photoelectric-converting) sunlight into electric power in each of the plurality of power satellites, and transmitting the electric power to a receiving antenna disposed in a specific location on the earth by converting the electric power into microwaves is under review.
The reason why instead of the plurality of power satellites, a single power satellite into which they are integrated is not provided is causing very upsizing of the power satellite and the impracticality from respect of implementation and reliability. In the case of sharing power generation among a plurality of power satellites, when the generating capacity is assumed to be equal to one million kW (corresponding to that of currently-functioning nuclear power plants), for example, about several hundreds of power satellites are needed. A microwave transmitted to the ground is spread over a range wide so that its energy density becomes small in consideration of safety (the energy density has to fall within the legal limit). An electric power base located on the earth includes a number of receiving antennas arranged in an area of several tens of square kilometers, receives incident microwaves by means of these receiving antennas, and integrates the received microwaves into high electric power.
In accordance with the method of receiving microwaves which above-mentioned prior art space photovoltaic power generation systems employ, a microwave beam from each of a plurality of power satellites arranged in space is concentrated onto a receiving antenna located on the earth. A problem with the microwave receiving method is therefore that if a plurality of microwaves from the plurality of power satellites are transmitted to the same region of the receiving antenna, the energy density of the microwaves incident on the region locally exceeds a legal limit because of the interference of microwaves as electromagnetic waves, even if the energy density of an individual microwave is small. Furthermore, another problem is that there is a need to increase the resistance of the receiving antenna to electric power since the energy of microwaves is concentrated onto part of the receiving antenna.
The present invention is proposed to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a method of and a system for receiving microwaves, capable of dispersively directing a plurality of microwave beams transmitted from a plurality of power satellites into different positions on a receiving antenna without concentrating a plurality of microwave beams from the plurality of power satellites onto the same region of the receiving antenna, so as to level the energy distribution of microwaves on the aperture surface of the receiving antenna.
In accordance with one aspect of the present invention, there is provided a method of receiving microwave beams from a plurality of power satellites in space by way of a receiving antenna, the method comprising the step of: by controlling a direction of each of a plurality of microwave beams to be transmitted from the plurality of power satellites, directing the plurality of microwave beams into an aperture surface of the receiving antenna so that the plurality of microwave beams are dispersively received at a number of different positions on the aperture surface of the receiving antenna, so as to level energy distribution of the microwaves received on the aperture surface of the receiving antenna.
In accordance with a preferred embodiment of the present invention, the method further comprises the steps of virtually defining a plurality of small regions on the aperture surface of the receiving antenna as the plurality of different positions, and controlling the direction of each of the plurality of microwave beams to be transmitted so that the plurality of microwave beams are directed into the plurality of small regions, respectively.
In accordance with another aspect of the present invention, there is provided a microwave receiving system comprising: a plurality of power satellites each for transmitting a microwave beam; a receiving antenna for receiving a plurality of microwave beams from the plurality of power satellites; and a control unit for controlling the plurality of power satellites so that the plurality of microwave beams are dispersively directed into a number of predetermined different positions on an aperture surface of the receiving antenna.
In accordance with a preferred embodiment of the present invention, the control unit controls the plurality of power satellites so that the microwave beam from each of the plurality of power satellites is directed into a corresponding one of the plurality of predetermined different positions on the aperture surface of the receiving antenna.
In accordance with another preferred embodiment of the present invention, the plurality of predetermined different positions are arranged uniformly on the aperture surface of the receiving antenna.
In accordance with a further preferred embodiment of the present invention, the control unit controls the direction of each of the plurality of microwave beams to be transmitted from the plurality of power satellites based on information on the plurality of predetermined different positions on the aperture surface of the receiving antenna.
In accordance with another preferred embodiment of the present invention, the control unit includes a location information transmission unit for transmitting the information on the plurality of predetermined different positions on the aperture surface of the receiving antenna, and a beam direction control unit for controlling the direction of each of the plurality of microwave beams to be transmitted from the plurality of power satellites based on the information transmitted by the location information transmission unit.
Preferably, the plurality of predetermined different positions are a plurality of small regions that are virtually defined on the aperture surface of the receiving antenna. In addition, the control unit can control the plurality of power satellites so that the microwave beam from each of the plurality of power satellites is directed into a corresponding one of the plurality of small regions on the aperture surface of the receiving antenna.
In accordance with a further preferred embodiment of the present invention, the control unit controls each of the plurality of power satellites so that the microwave beam from each of the plurality of power satellites is directed into a different one of the plurality of small regions on the aperture surface of the receiving antenna.
In accordance with another preferred embodiment of the present invention, a number of the plurality of power satellites is equal to a number of the plurality of small regions, and the control unit controls each of the plurality of power satellites so that the microwave from each of the plurality of power satellites is directed into a different one of the plurality of small regions on the aperture surface of the receiving antenna.
In accordance with a further preferred embodiment of the present invention, the plurality of power satellites is divided into a number of groups, and a number of the plurality of groups is equal to a number of the plurality of small regions. In addition, the control unit can control each of the plurality of power satellites so that a microwave beam from each of the plurality of groups is directed into a different one of the plurality of small regions on the aperture surface of the receiving antenna.
In accordance with another preferred embodiment of the present invention, the plurality of small regions include a plurality of first small regions into which the aperture surface is divided so that they do not overlap one another, and a plurality of second small regions which do not overlap one another and each of which is located at a boundary between first small regions adjacent to each other.
Preferably, the receiving antenna is an array antenna including a plurality of antenna elements arranged in a form of an array.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.